Full disclosure, I am an atheist. However that being said if I came to believe in the Christian God I would have no idea--and no way to find out with any certainty--which Christian religion is the true religion. Some Christian denominations preach that failure to believe in their dogma would bar me from heaven, and damn me to hell or its equivalent.
The true Christian is one who is in Christ, the teachings of Christ and the belief of a Christian are one. If what one who professes to be a Christian teaches is contrary to the teachings of Christ... then that individual is not a Christian. That is how you find out "with certainty".
So, I wonder, how does any Christian know with any certainty that they are on the right path to salvation? It seems to me no Christian can be even reasonably sure that, despite their belief in God and Jesus, that they can be assured of anything after death like everlasting life, given the enormous disagreement between Christians. If Christians can't agree on how to be a Christian and honor, worship, and serve God, how is a converted atheist supposed to choose (and choose one must some Christian denominations claim) which is the correct path?
"For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life." (John 3:16)
"But God commendeth his love toward us, in that, while we were yet sinners. Christ died for us." (Romans 5:8)
"That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved." (Romans 10:9)
How, I wonder, can any Christian be believed? How can one know who is right and who is wrong?
You know what is Evil, if one teaches that you should do evil, then they serve evil. If one teaches that you should do good, then they serve what is good.... and only God is good.
It seems to me that every Christian, no matter how true their faith, is condemned to their own insoluble Pascal's Wager. They cannot know the true faith. How awful, it seems to me, to know that despite a belief in God and Jesus and faithfully serving them both that a Christian can still suffer internal damnation for merely failing to choose the right Christian religion.
I confess Christ, and my sin. I am saved as a result of the grace of God, according to the scriptures which are the foundation, beginning and end. Christ taught that If I am a believer then I am saved, I am a Christian because I believe in what Christ taught.... therefore you are just babbling.